Process for casehardening hollow metal members



April 23, 1946. c. L. SNYDER 2,398,809

PROCESS FOR CASE HARDENING HOLLOW METAL MEMBERS Filed Aug. 26, 1944 I N VZIN TOR. Eggs/0112 Z. Snyder Q i g C HTTOIPNEYI Patented Apr. 23, 1946- raocass roa oasnrmannma noLLow METAL MEMBERS Christopher L. Snyder, Metuchen, N. 1., asslgnor to steatite Research Corporation, a corporation of Delaware Application August as, 1944, Serial No. 551,325

18 Claims.

This invention relates to a process for case hardening hollow metal members and has for an object an improved process for case hardening the exterior of such articles while leaving the interior surfaces untreated.

In case hardening bushings, wrist pins, sleeves, and similar hollow members wherein it is desirable to have a hardened exterior surface and a comparatively soft but tough interior, it is the general practice to drive a close-fitting steel plug into each end of the hollow member and to seal the Joint therebetween by cementing the same with a specially prepared cement. The resultant plugged member is next passed through a carburizing process, for the purpose of adding carbon to the exposed surfaces, which includes heating the member to a comparatively high temperature, and then quenching, usually by dipping into a liquid, in order to harden the exposed surfaces. Upon removal from the quenching liquid the steel plugs are removed from the hollow member and cleaned for further similar use.

It has been suggested in a process for case hardening apertured members/that the apertures be sealed prior to the carburizing process by first driving ceramic plugs therein and then cementing the Joints formed between the plug and member surfaces with a specially prepared cement. Since the cementing step does not always Produce the desired seal, particularly during the high tem, peratures of carburization, improved sealing means over the above have been sought in order to minimize production of defective articles.

It is, therefore, an object .of this inventionto eliminate the above cementing step and to devise an improved method for sealing joints.

A further object of the invention is to provide a ceramic sealing means, the sealing characteristics of which improve as the carburizing process proceeds.

A still further object of the invention is to provide a ceramic joint sealing means which fuses into a viscous mass during the carburizing process and adheres more effectively to the materials being joined.

According to a feature of the present invention advantages are secured over the above cement sealing method by firstcoating the ceramic plug with a glaze and, while the glaze is still in its green or unfired state, forcing the plug into the opening to be sealed. During the carburizing ceramic and metallic surfaces, thereby forming a more perfect seal.

According to another feature of the invention process the laze matures and adheres to both the ceramic plug is preflred with a glaze thereon and then forced into the opening to be sealed. During the carburizing process the glaze fuses and adheres to both the ceramic and metallic surfaces, thereby forming an eifective seal.

These and other features of the invention will Referring now to the drawing, there is shown a hollow member l0, such as a wrist pin or the like, the exterior surface only of which is to be case hardened. In order to maintain a soft but tough interior surface it is required that no carbon be permitted to enter within the interior of the wrist pin l0 during the carburizing process, which will be described hereinafter, and consequently the openings thereof must be thoroughly sealed. This seal must be effective through a broad range of temperatures, which'may go from normal room temperatures to as high as about 1800 F. Although the member I0 is shown as provided with two open ends. it is understood, of ,course, that this invention is'not to be restricted to'sealing this number of open ends, a it may be applied to a member having only one or any plurality of openings. Furthermore, the member ID may have any desired form.

An effective and inexpensive sealing means for the wrist pin I0 is provided by any satisfactorilyshaped plug H, such as a frustum-shaped plug of ceramic material. Although any suitable composition of ceramic material may be employed for Clay 5- 20%, preferably about 15% Talc -90%. preferably about BaCOa and/or CaCOa; 1-20%, preferably about 5% To provide a still more effective sealing means the plug II is coated with a glaze I! of any suitable composition, such as follows:

The above composition is then mixed with a suitable organic binder, for example, 5% of. dextrin; which is consumed during the heating process.

Any ceramic material having the proper density and the proper co-efllcient of expansion may be used in this process. It is to be noted that the glaze l2 with its organic binder forms a cushion between the ceramic plug II and the contacting metallic interior of the wrist pin Ill and thereby forms a more perfectly sealed Joint.

It is a characteristic of the green or unfired laze I2 that during the carburizing process the glaze matures, that is, it fuses to a highly viscous mass which adheres to both the pre-fired'plug I I and to the metallic surface of the wrist pin [0. It is a characteristic also of pre-fired glaze that, when subjected to the high temperatures employed in the carburizing process, it likewise fuses into a viscous mass. This viscous mass thus provides a good seal for the range of temperatures encountered during the carburizing process.

It is an inherent property of both the glaze I2 and plug II that upon being heated to a high temperature and then suddenly cooled, the glazed seal will immediately break and the plug will disintegrate. This property is utilized in this invention for facilitating removal of the plug II from the processed member Ill.

The case hardening process of the invention will nowbe described. The first step consists in coating a.ceramic plug II, which has been prefired and which has the above-described properties, with a glaze H of the hereinbefore-described properties, I Next, such a glazed plug ii is driven into each end of the wrist pin i until satisfactory joints between the plug and wrist pin surfaces are provided, while the glaze is still in its green or unfired state. As an alternative for the first step, the plug ll may be pre-fired with the glaze i2 previously applied thereto. The plugged wrist pin assembly is then put through any of the well-known carburizing processes by heating it to relatively high temperatures usually within the range of 1600 F. to 1800 F., for a predetermined interval in contact with carbonbearing materials, such as gases, liquids, or solids, that are capable of'yielding carbon to the exposed metallic surface. It is a particular feature of the sealing means used herein that as the temperature increases the glaze becomes viscous,

- and, as a result, more effectively seals or locks the inner surface of the member It with the contacting surface of plug i i,

Following the carburizing treatment the heated assembly is dipped into a quenching solution or coolant, such as water, brine, or oil of substantially lower temperature for hardening the outer surface thereof. Immediately upon immersion into the solution the seals between the surfaces of the plugs II and pin it) are severed and the plugs Ii crumble to pieces. ily seen that removal of the ceramic plug H, as practised in this invention, is a substantial improvement over the steel-plug-removing step of the prior practice; and inasmuch as the glazed plug H is comparatively inexpensive further economies are obtained. Moreover, since the plug is only used in one case hardening operation, a better fit, and at the same time a better seal, may be obtained, thereby minimizing the number of defectively case hardened articles. The effectivity of the seal is greatly enhanced by the viscous nature of the glaze sealing material which fiows in to close any crevice which may be formed due to a poor fit of the plug in the opening.

While this invention has been shown and described as embodying certain features merely for the purpose of illustration, it is, 01! course,

It can thus be readunderstood that various .modifications may be made in the process thereof without departing from the scope of the invention as defined in the appended claims. For example, ceramic caps, instead of plugs, may be employed for sealing metallic members.

What is claimed is:

1. The method of case hardening the exterior surface of a metallic member having at least one opening therein, which consists in sealing said opening by glaze-coated ceramic means, carburizing the member, and quenching the carburized member while hot, whereby the ceramic seal is automatically broken.

2. The method of case hardening the exterior surface of a metallic member having at least one opening therein, which consists in sealing said opening by means including a glaze-coated ceramic element, carburizing the member, and quenching the carburized member while hot, whereby the,ceramic element is automatically broken.

3. The method of case hardening the exterior surface of a metallic member having a plurality of openings therein, which consists in sealing said openings by means ceramic plugs, carburizing the member, and quenching the sealed carburized member while hot, whereby the ceramic plugs are automatically disintegrated.

' 4. The method of case hardening the exterior portion of a hollow metallic member having at least one opening therein, which consists in sealing said opening by means including a glazecoated ceramic cap, passing the capped member through a carburizing process, and quenching the carburized member while hot in a. liquid of substantially lower temperature, whereby the ceramic cap crumbles during the quenching operation.

5. The method of case hardening the exterior portion of a hollow metallic member having at least one opening therein, which. consists in sealing said opening by means including a glazecoated ceramic element, passing the sealed member through a carburizing process, and quench-- ing the carburized member while hot in a liquid of substantially lower temperature, whereby the ceramic element crumbles upon immersion into the quenching liquid.

6. The method of case hardening the exterior portion of a hollow metallic member having at least one openingtherein, which consists in sealing said opening by means including a glazecoated ceramic plug, passing the plugged member through a carburizing process that includes heating the member to a substantially high temperature, and hardening the carburized member by quenching it in a liquid of substantially lower temperature, whereby the ceramic plug shatters during the quenching operation.

'7. The method of case hardening the exposed surf-ace of a hollow metallic member having a plurality of openings therein, which consists in sealing said openings by means including glazecoated ceramic plugs, passing the plugged member through a carburizing process that includes heating the member to a substantially high temperature, and hardening the carburized member by quenching it in a liquid of substantially lower temperature, whereby the ceramic plugs are disintegrated by the sudden change in temperature and separated from the metallic member.

' 8. The method of case hardening the exterior portion of a metallic member having at least including glaze-coated one opening therein, which comprises coating a ceramic element with a glaze, forcing the glazed element into said opening, carburizing the member, and quenching the carburized member, whereby the glazed joint between the element and member surfaces is automatically broken during the quenching operation.

9. The method of case hardening the exterior portion of a metallic member having at least one opening therein, which comprises coating a steatite element with a glaze, forcing the glazed element into said opening, carburizing the member, and quenching the carburized member, whereby the glazed joint formed between the element and member surfaces is automatically broken during the quenching operation.

10. The method of case hardening the exterior portion of a metallic member having at least one opening therein, which comprises coating a ceramieelement with a glaze, forcing the glazed element into said opening to provide a sealed joint between the element and member surfaces, carburizing the member, and quenching the carburized member, whereby the ceramic element is automatically broken during the quenching operation.

11. The method of case hardening the exterior portion of a metallic member having at least one opening therein, which consists in coating a steatite plug with a steatite glaze, forcing the plug into said opening to provide a sealed joint between the plug and member surfaces, carburizing the member, and quenching the plugged carburized member, whereby the ceramic plug is automatically broken during the quenching operation.

12. The method of case hardening the exterior portion of a metallic member having a plurality of openings therein, which consists incoating a plurality of steatite caps with steatite glaze, forcing the caps while the glaze is still in the green state over said openings to provide sealed joints between the cap and member surfaces, carburizing the capped member, and quenching the carburized member while hot in-a liquid of substantially lower temperature, whereby the joints are automatically broken during the quenching operation.

13. The method of case hardening the exterior portion of a hollow metallic member having a plurality of openings therein, which consists in coating a plurality of steatite plugs with steatite glaze; forcing the plugs, while the glaze is still in the green state, into said openings to provide ,sealed joints between the plugand member surfaces; carburizing the plugged member; and quenching the carburized member in a liquid of substantially lower temperature, whereby the steatite plugs disintegrate upon immersion into the quenching liquid.

14. The method of case hardening the exterior portion of a hollow metallic member having at least one opening therein, which consists in applying a coat of steatite glaze to the outer peripheral surface of a steatite plug; forcing the plug, while the glaze is still in its green state, into said opening to provide a sealed joint between the plug and member surfaces; passing the plugged member through a carburizing process that includes heating the member to a substantially high temperature, sothat the glaze fuses into a viscous mass; and hardening the carburized member by quenching it in a liquid of substantially lower temperature, whereby the steatite plug disintegrates upon immersion into the quenching liquid.

15. The method of case hardening the exterior portion of a hollow metallic member having a plurality of openings therein, which comprises applyinga coat of steatite glaze to a plurality of steatite plugs; forcing the plugs, whilethe glaze is still in the green state, into said openings to provide sealed joints between the plug and member surfaces; passing the plugged member through a carburizing process that-includes heating the member to a substantially high temperature, whereby the green glaze matures and provides more effectively sealed joints; and hardening the carburized-member by quenching it in a liquid of substantially lower temperature, whereby the steatite plugs disintegrate upon immersion into 'the quenching liquid.

16. The method of case hardening the exterior portion of a metallic member having at least one opening therein, which comprises coating a ceramic element with a glaze, firing the glazecoated element, forcing the glazed element into said opening, carburizing the member, so that the glaze fuses into a viscous mass to more effectively seal the element and member surfaces, and

quenching the carburized member, whereby the glazed joint between the element and member surfaces is automatically broken during the quenching operation. i

17. The method of case hardening the exterior portion of a metallic member having at least one opening therein, which comprises coating a steatite element with a glaze, firing the glazecoated element, forcing the glazed element into said opening, carburizing the member, so that the glaze fuses into a viscous mass to more effectively seal the element and member surfaces, and quenching the carburized member, whereby the glazed joint formed between the element and member surfaces is automatically broken during the quenching operation.

18. The method of case hardening the exterior portion of a hollow metallic member having a plurality of openings therein, which comprises applying a coat of steatite glaze to a plurality of steatite plugs; firing the glaze-coated plugs; forcing the glazed plugs into said openings to provide sealed joints between the plug and member surfaces; passing the plugged member through a carburizing process that includes heating the member to a substantially high temperature, whereby the glaze fuses into a viscous mass and provides more effectively sealed joints; and hardening the carburized member by quenching it in a liquid of substantially lower temperature, whereby the steatite plugs disintegrate upon immersion into the quenching liquid.

CHRISTOPHER Ia. SNYDER. 

